In the sport of drag racing motor vehicles, centrifugal clutches have dominated motorcycles and specialized mechanical clutches are normally employed in dragsters. Developments to improve either type of clutch have been continually pursued in the industry and adaption is made very rapidly to eliminate any competitive advantage. Conventional clutches normally utilized in motorcycles are operated manually by a lever mounted on the handlebar with cable and rack and pinion operator. The coordination of increasing speed with the accelerator and releasing the clutch at the appropriate engine rotational speed has proven by itself to be ineffective and somewhat erratic. Centrifugal clutches have dominated the field due to their superiority in regulated speed engagement and slip control. Dry types of clutches have been tried in the past using materials with a high coefficient of friction specifically for this purpose, however, extensive modification to the vehicle, particularly a motorcycle, makes this approach expensive and time consuming.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however, the following U.S. patents are considered related:
______________________________________ U.S. PAT. NO. INVENTOR ISSUE DATE ______________________________________ 5,033,598 Tipton Jul. 23, 1991 4,989,711 Schultz et al Feb. 5, 1991 4,986,403 Tipton Jan. 22, 1991 4,856,637 Gebhart Aug. 15, 1989 4,732,251 Tipton Mar. 22, 1988 4,566,577 Tsuboi Jan. 28, 1986 4,111,291 Horstman Sep. 5, 1976 1,743,170 Vail Jan. 14, 1930 1,035,535 Coleman Aug. 13, 1912 ______________________________________
Tipton in patent '598, issued to the present inventor, teaches an improvement in motorcycle slider clutches that utilizes several original equipment manufacturer's components and an aftermarket basket assembly. An enclosure surrounds the basket and fingers operated centrifugally that compress the clutch discs and plates in the first stage of operation. The second stage is electrically timed in sequence utilizing pressurized fluid to control the action of the cammed fingers in a positive actuating mode of operation.
Schultz et al, patent '711, discloses a controller for a centrifugal clutch with weighted arms. The controller has a fluid actuated cylinder and piston engaging a throw out bearing. The controller is pre-programmed to restrain pivoting the arms and weights to slow and control the rate of increase of actuating pressure in the clutch.
Tipton's patent '403, issued to the present inventor, is for a motorcycle slider clutch that utilizes a pair of pneumatic cylinders and pistons to restrain the movement of centrifugally actuated fingers creating multi-stage control. Solenoid valves and timers allow a timed starting sequence with the centrifugal slider clutch utilizing a number of original equipment manufacturer's components and aftermarket modifications.
Gebhart, in patent '637, teaches a centrifugal clutch with a frusto-conical friction surface with drum and levers adapted to bias the conical surface at a predetermined speed of rotation. Stall speed screws adjust the speed of rotation for engagement and drive torque is transmitted by a sprocket attached to the pressure drum. The shape of the pressure plate creates an increased mechanical advantage permitting a reduced physical size.
Patent '251, also issued to the present inventor, utilizes a portion of the original equipment manufacturer's components, however, it is directed to an entirely centrifugal actuated clutch using new elements to change over from the mechanical type. Fingers and a pressure plate are added to force the plate into contact with the original discs and plates making a union between the rotating elements due to the centrifugal force applied by the fingers. The clutch is wet being oil lubricated in the same manner as originally designed by the manufacturer.
Tsuboi, in '577, discloses a clutch release device for motorcycles using a manual actuated hydraulic system in which a push rod is arranged to extend through the main shaft with a pressure plate on each end. One end is arranged to interface with a hydraulic cylinder and the other with the clutch disc pressure plate. It is noted, however, that no centrifugal action is used by this invention and it is assigned to the motorcycle original equipment manufacturer.
Horstman, in '291, teaches a centrifugal clutch for go-carts and employs weights or stampings that pivot against a plate compressing discs together for engagement, depending upon rotational speed.
Vail, in '170, uses centrifugal weights forcing separable plates together against adjustable spring pressure, further allowing manually operated means to relieve the pressure on the weights forcing them into an inoperable position allowing shifting of gears.
For background purposes and as indicative of the art to which the invention relates reference may be made to the patent issued to Coleman.